[PlanarReflection] Removed incorrect include

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/materialflags.compute

 #define UNITY_MATERIAL_LIT // Need to be define before including Material.hlsl
 #include "../../Material/Material.hlsl" // This includes Material.hlsl
 #include "../../Lighting/LightDefinition.cs.hlsl"
-#include "../../Lighting/LightDefinition.custom.hlsl"
 
 #define USE_MATERIAL_FEATURE_FLAGS
 #define NR_THREADS	64

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightUtilities.hlsl

 #define UNITY_LIGHT_UTILITIES_INCLUDED
 
 #include "LightDefinition.cs.hlsl"
-#include "LightDefinition.custom.hlsl"
 
 // The EnvLightData of the sky light contains a bunch of compile-time constants.
 // This function sets them directly to allow the compiler to propagate them and optimize the code.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScattering.compute

 #include "CoreRP/ShaderLibrary/SpaceFillingCurves.hlsl"
 #include "../../ShaderVariables.hlsl"
 #include "../../Lighting/LightDefinition.cs.hlsl"
-#include "../../Lighting/LightDefinition.custom.hlsl"
 #include "SubsurfaceScattering.hlsl"
 
 //--------------------------------------------------------------------------------------------------

ScriptableRenderPipeline/HDRenderPipeline/HDRP/RenderPipelineResources/CopyStencilBuffer.shader

     #include "CoreRP/ShaderLibrary/Packing.hlsl"
     #include "../ShaderVariables.hlsl"
     #include "../Lighting/LightDefinition.cs.hlsl"
-    #include "../Lighting/LightDefinition.custom.hlsl"
 
     int _StencilRef;
     RW_TEXTURE2D(float, _HTile); // DXGI_FORMAT_R8_UINT is not supported by Unity